introduce kref_put_mutex()

equivalent of
	mutex_lock(mutex);
	if (!kref_put(kref, release))
		mutex_unlock(mutex);

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/include/linux/kref.h b/include/linux/kref.h
index 9c07dce..65af688 100644 (file)
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -18,6 +18,7 @@
 #include <linux/bug.h>
 #include <linux/atomic.h>
 #include <linux/kernel.h>
+#include <linux/mutex.h>
 
 struct kref {
        atomic_t refcount;
@@ -93,4 +94,21 @@ static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)
 {
        return kref_sub(kref, 1, release);
 }
+
+static inline int kref_put_mutex(struct kref *kref,
+                                void (*release)(struct kref *kref),
+                                struct mutex *lock)
+{
+       WARN_ON(release == NULL);
+        if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) {
+               mutex_lock(lock);
+               if (unlikely(!atomic_dec_and_test(&kref->refcount))) {
+                       mutex_unlock(lock);
+                       return 0;
+               }
+               release(kref);
+               return 1;
+       }
+       return 0;
+}
 #endif /* _KREF_H_ */